Chemical and metallurgical aspects of arsenical bronze: the case of arsenic-loss in prehistoric metal production

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After annealing and deformation of a lot of samples, I am busy with polishing. Polishing of a lot of samples. Also, the next article on ‘Arsenical bronze: a constant out-of-equilibrium’ is almost ready for submission. Further articles on the loss of arsenic during recycling activities, and on the colour of arsenical bronze, are in preparation.

Slightly over a century ago, poison was a common part of everyday life. Arsenic, the notorious metalloid, was used in all sorts of products, primarily in the inks and aniline dyes of beautifully printed wallpapers and clothing. Odorless and colorless, it went into food as food coloring, and it was used in beauty products, such as arsenic complexion wafers that promised women pure white skin, until as late as the 1920s. It was found in the fabric of baby carriages, plant fertilizers, medicines. It even was taken as a libido pill in Austria.

The literature of the era hints at the effects from arsenic poisoning. The main character in Charlotte Perkins Gilman’s 1892 short story “The Yellow Wallpaper,” for instance, descends into madness and believes that the source of her illness stems from the wallpaper in her room. “It makes me think of all the yellow things I ever saw—not beautiful ones like buttercups, but old foul, bad yellow things,” she says. “But there is something else about that paper—the smell!”There are numerous studies on William Morris’s arsenic-laden wallpapers, in particular, which were extremely popular during the late 19th century. Morris himself, a designer and artist, was also the heir to the world’s largest copper mine at the time, which produced arsenic dust due to mining activity. Not only did the mine cause massive environmental damage to the land around it, but many miners died of lung disease, according to a 2003 article in Nature. Morris’s famous phrase about the doctors who treated these miners was that they “were bitten by witch fever,” insinuating that the doctors were quacks when they diagnosed arsenic poisonings. He was unwilling to believe the catastrophe his businesses had caused.
As long as people get what they want, most people don’t think twice about it.

Using Morris’s phrase as a fitting title, the art historian and Victorianist Lucinda Hawksley’s new book, Bitten by Witch Fever, tells the story of the extensive use of arsenic in the 19th century. It includes pictures of objects and artworks made from substances that incorporated arsenic, and advertisements for arsenic-filled products for Victorian women, such as soap with a doctor’s certificate to ensure its harmlessness.I spoke to Hawksley about arsenic’s prevalence in 19th-century home decoration, clothing, food, and topsoil. Our conversation has been condensed and edited for clarity.

Haniya Rae: Why was arsenic so commonly used?Lucinda Hawksley: In mid-Victorian times, Pre-Raphaelite and Aesthetic artists were particularly sold on this vivid shade of green, found by the Swedish chemist Carl Wilhelm Scheele in the 18th century. The green color came from copper arsenite, known as Scheele’s Green, which is a form of arsenic and a byproduct of the copper industry.If you think about the brilliance of copper and the way that a patina begins to color metal, it’s a beautiful color. Chemists hadn’t thought about how poisonous arsenic was, which today would seem crazy to us—it was present in so many things. Victorians didn’t think it was a problem unless you ate it. They hadn’t made the connection that the same thing that created this amazing green, and that was immensely fashionable in the 1860s and 1870s, could be a problem. It wasn’t just the Victorians, though—Germany, the United States, Scandinavia, among others, were all using arsenic in common goods.

Rae: By the late Victorian period, though, people had started to figure out it was dangerous?Hawksley: Around the 1860s, the cases of arsenic poisoning started getting to the newspapers. One wallpaper manufacturer debuted arsenic-free wallpaper, but no one paid much attention to that, until more and more cases started appearing. By the 1870s, William Morris started to produce arsenic-free wallpapers. At this point, William Morris himself didn’t actually believe that the arsenic was the problem—he was simply bowing to public pressure. He thought because no one was ill in his house from the arsenic wallpaper, it must be something else that was causing the sickness.

Rae: What were a few of these cases?Hawksley: Factory workers were getting sick—and many died—because they were working with green arsenic dye. It was fashionable to wear these artificial green wreaths of plants and flowers in your hair that were dyed with arsenic. In wallpaper factories, workers were becoming really unwell, especially when they were working with flock papers, or papers with small fiber particles that stick to the surface. The workers would dye these tiny, tiny pieces of wool or cotton in green, and while doing so would inhale them and the particles would stick to their lungs. The manufacturing process created a lot of dust from the dye—the dust had arsenic in it—and this created major problems for the factory workers as the dust would stick to their eyes and skin. If there were abrasions on their skin, the arsenic could get directly into their blood stream and poison them that way as well.

When the newspapers started to point out that this was happening, most people didn’t care. It’s a bit like today. People will still buy a brand of chocolate even if there’s been a story on how the chocolate has been produced by slave labor. They buy coffee that was also produced by slaves. They buy clothes, even though it was made by bonded labor. As long as people get what they want, most people don’t think twice about it. If they were confronted with things face on, of course they wouldn’t buy these products.

Rae: Did Britain ever pass legislation about arsenic?

Hawksley: In 1903 century, the U.K. actually did pass legislation about the safe levels of arsenic levels in food and drink—even though often there are no safe levels at all—but Britain never passed laws around wallpaper or paint. By the time the regulations were passed on arsenic in food and drink, arsenic wallpaper and paint had fallen out of fashion, so it’s possible they didn’t see a reason to actually pass legislation against it. To this day, there still isn’t a law banning someone from making arsenic wallpaper or dye in Britain.Rae: But it was pretty bad before that point?Hawksley: Before legislation was passed, bakers used arsenic green as a popular food coloring. Sometimes, a baker was given flour or sugar with arsenic in it unknowingly, but other times it was used as a bulking agent. You wouldn’t believe the kinds of things that were put into Victorian foods as bulking agents. It wasn’t just arsenic, there were lots of weird things. Flour was expensive, so they would resort to adding other things.There was an orphanage in Boston and all these small children were getting really, really sick and they didn’t know why. It turned out that the nurses were wearing blue uniforms dyed with arsenic and they were cradling the children, who in turn were inhaling the dye particles.That’s another thing, too: Green was a color that was always seen as the culprit, simply because it was so desirable at the time, but many other colors used arsenic as well. When the National Archives did testing on the William Morris wallpapers, all of the colors used arsenic to some extent. These colors were exceptionally beautiful, and up until this point, it was not something they could achieve without the use of arsenic.Rae: Are there still remnants of arsenic mining today?Hawksley: It’s funny because as I was doing my research, I was having a conversation with an older woman about my work. She had memories of growing up in the 1930s near a town that had had a working copper mine nearby. Her mother had told her not to grow any vegetables, because at that time they had realized the dangers of arsenic dust and knew it was in the soil. But for a long time, people living near copper mines had no idea that arsenic dust was falling on the soil, and so their crops would absorb all this arsenic dust. Lots of people were getting sick, but no one seemed to understand why. I’m sure that must have been the case with mining like this all over the world.

The last weeks I was busy with preparing roughly 300 samples for the data base and the hardness measurements. Samples were made of eight different alloys, four different annealing times at 600°C in reduced atmosphere, cross-section and longitudinal section, and up to five different grades of deformation (cold rolling). And I have to admit that the rolling machine is just fantastic! The more arsenic the alloy contains, the harder it was to roll (not very surprising…) but I was fascinated by the squeaky sound the higher alloyed metal produced.

Finally, the project’s first article A Re-evaluation of inverse segregation in prehistoric As-Cu objects is out (others will follow soon). It’s published in the current issue of The Journal of Archaeological Science.You can get your free copy until November 1st, 2016, here. Enjoy!

The study revaluates reported cases of prehistoric As-Cu objects with ‘silvery surfaces’, which are usually interpreted as the result of inverse segregation. Further possible explanations for such surfaces, such as an arsenic-rich alpha-solid solution, cementation, or post-depositional precipitation, are discussed. The segregation of arsenic was studied in As-Cu ingots produced in chill cast moulds at several compositions, which underwent surface treatment with an NaCl solution. The microstructure and surfaces of the As-Cu alloys were analysed using optical microscopy and SEM-EDXS. Special note of out-of-equilibrium As-Cu phases are discussed, as well as a comparison of inverse segregation to all other means of achieving surface silvering.

After November 1st, 2016, you can have access to the article via academia, or just send me an email.

This time, it is bacteria eating arsenic. To be more precise: especially ectothiorhodospira-like purple bacteria or oscillatoria-like cyanobacteri are using arsenite as an energy source. The light-dependent oxidation of arsenite [As(III)] to arsenate [As(V)] occurrs under anoxic conditions. The recently discovered bacteria from oxygen-free hot springs in Mono Lake, California, suggest that the arsenic metabolism / photosynthesis evolved at the same time, or even before, ‘normal’ photosynthesis.

We just should not add nano-size rust particles to their food. Arsenic binds particularly well to iron oxides, or rust, and can be consequently easily removed by nano-size rust particles. Such particles can be easily produced by simmering (olive/oleic) oil and rust in a frying pan, which might be a cheap way to remove arsenic from drinking water, which presence there is still a very big problem in Bangladesh or West Bengal (and it seems also in Cornwall, UK). The clumped together arsenic and rust can be easily removed with a magnet.

Young gentoo penguins on Peterman Island (c) Wikipedia

Discussing arsenic in food and drinking water brings us consequently also to end-product of digestion. And penguins, in particular Gentoo penguins. Both together are the main source of arsenic accumulation in Antarctic soil. The droppings of this type of penguin contained far more arsenic than those of other species, such as the droppings of the southern giant petrel and up to three times more than the local seals. Consequently, the sediments of other Antarctic islands without resident penguins (but similar geology) contain half the levels of arsenic compared with sediment sampled on Ardley Island, where these penguins live. Since arsenic is present in the water, which is absorbed by krill and then accumulates in the food chain, passing to predators such as penguins, the arsenic levels measured in Antarctic soil can be used as an indicator of past (Gentoo) penguin populations: the more arsenic, the more penguins.

Arsenical bronze with 11 wt.% arsenic after cooling down with 20 K/min. Note the inverse segregation at the edge, and the massive appearance of (α+γ) eutectic.

The DTA analyses started in February 2016 are finished, and an out of equilibrium phase diagram for the Cu-As system up to 15 wt.% arsenic was established. One of the characteristics of the diagram is also the appearance (even below 2 wt.% of arsenic) and temperature changes of the (α+γ) eutectic. I am currently preparing the article, which, once accepted, will be posted here. I noted also some losses in arsenic, which are mainly the result of adding the arsenic lump to the molten copper.

Recently started analyses with the DTA-TGA instead show significant losses of arsenic when melting the alloy, and less once it is cooling down. I am thrilled to see more results and curves, and to figure out how to connect them with the loss of arsenic during prehistoric recycling activities!

Following an invitation of the University of Cork, I was able to visit the Ross Island copper mines beginning of March.

The prehistoric copper mines, which date back as far as 2400 BC, are located in the Killarney National Park. The mines are situated at the shore of the lake on an peninsula, less than half an hour walk from Ross Castle, a 15th century fortress. One can arrive to the mines by following a trail, passing through swamp and a wild forest, and the area of recent mining activity from the 19th century.

It is still possitble to see lots of traces from prehistoric mining on site, such as working ‘tables’, grinding stones, and remnants of fire setting. Unfortunately, the full extend of the underground mining is not anymore accessible today due to floods and roof collapses. Ceramic found on site connect the mining site with the Beaker material culture. Close to the mines, just a few meters higher above the lake, the miner’s work camp, which was only seasonally used, was found. Here, the minerals were crushed, hand-sorted, and smelted in shallow pit furnaces. No slags were found. The ingots produced were then transported to the nearby settlements and cast into other objects.

The arsenic content of the main copper mineral mined, tennantite, reaches up to 20%. Of course most of it was reduced during smelting, but the final objects still show significant amounts of arsenic (1-5 wt.%) and a distinctive impurity pattern (As>Sb>Ag). This, and the high amounts of arsenic, can be traced in the so-called ‘A’-copper, which circulated widely in Ireland in the period 2400-1900 BC, and also reached Britain. Ross Island is so far the only Irish copper mine with prehistoric mining known with such high amounts of arsenic, and is consequently most likely the source of this ‘A’-copper, which makes it the oldest known mine in Ireland.

After my presentation, we visited Ross Island with Prof. William O’Brien. Wind, rain, and temperatures below -10°C (at least that what it felt like for me) did not stop us to collect some tennantite, which I intend to use for several smelting and melting experiments.

Ross Island, relicts of prehistoric copper mining activities.

…the minerals collected were good, as I realised the next day at the costums at Dublin airport: security stopped me to see which kind of strange metals I have in my bag. Should be at least 40% copper, they said. I am going to figure that out soon!

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Marianne Mödlinger

Marianne Mödlinger is a prehistoric archaeologist. Her main research interests include Bronze Age studies, the manufacture and usage of Bronze Age arms and armour, archaeometallurgy of copper alloys, and experimental archaeology.